Thermal treatment of gases and vapors



May 28, 1935. A. CAMERON ET AL 2,002,525

THERMAL TREATMENT OF GASES AND VAPOBS Original Filed Feb. 23, 1933INVENTQRS A.CAMBRON and CJ'LBAYLEY BY ATTOR NEY.

Patented May 23, 1935 UNITED STATES THERMAL TREATMENT OF GASES AND VAPOBS

Adrien Cambron and Colin Hahnemann Bayley,

Ottawa, Ontario, Canada Original application February 23,1933, SerialNo. 658,098. Divided and this application January 31, 1934, Serial No.709,202. In Canada February 18, 1933 4 Claims.

This invention relates to the thermal treatment of gases or vapors toproduce desired chemical reactions and, more particularly, to thethermal treatment of lower paraffln hydrocar- 5 bons in the gas or vaporphase for the produc-. tion of products containing high percentages ofvaluable unsaturated hydrocarbons, such as olefines.

It is well known, for example, that, when heated to a suitabletemperature, the lower paraflins having more than one carbon atom areconverted into a mixture of olefines, hydrogen, parafiins having a lowernumber of carbon atoms, and unchanged paraflins. Complete conversion ofethane or propane, for example, would give a product containing 50% ofolefines by volume but, when using heretofore known pro- 'cessses, themaximum concentration is never even (nearly) approached without theformation of by-products such as liquid hydrocarbons, tarand freecarbon. The formation of free carbon is particularly objectionable as itcauses frequent interruption of the operation of the process to cleanout the reaction tubes, reduces the ,yield of olefines and limits thetemperature at which the process can be economically operated.

The object of the present invention is to provide a process andapparatus whereby such endothermic reactions may be carried out withgreater efiiciency, producing higher yields of the desired products andwithout substantial formation of objectionable by,products, whichreduces the yield of the desired product, lowers the efficiency of theprocess and limits the temperature at which it can be economicallyoperated.

A further object of the invention is to provide temperature of the gasor vapor, in order to secure economical conversion of the paraflins toolefines or other desired products.

The invention will now be described with reference'to the accompanyingdrawing, in which- Figure 1 is a longitudinal section on line |l ofFigure 2;

Figure 2 is a cross section .on line 2-2 of Figure l; and Figures 3 and4 show diagrammatically alternate forms of the reaction tube.

In the drawing, l represents the reaction tube, which may be heated inany desired way, as by a heating coil 2 connected to an electric powerline 3. An ammeter is shown at 4. A thermo-.

couple 5 is connected with a millivoltmeter 6. 1 represents any desiredform of insulation about the heating coil and tube. A rod 8 is centrallydisposed within the reaction tube by means of supports 9. On this rodare located, perpendicularly to the rod, a plurality of spaced bafflesl0 having a diameter somewhat less than the internal diameter of thetube. The baiile diameter is preferably substantially 0.8 to 0.9 of thetube diameter and the baffle spacing on the rod is preferablysubstantially 0.5 to 1.0 of the tube diameter. The tube has a gas inletII and an outlet l2.

In the reaction tube illustrated in Figure 3 the support 8 is tubularand the gas is admitted through the tubular support at I I, entering thereaction zone at I3 and the products are discharged at'the outlet l2. Inthe illustration of Figure 4 the support 8 is also tubular and throughit a stream of water or steam may be passed countercurrent to the flowof gases in the reaction zone. These forms of the apparatus maybe usedwith advantage, particularly where the reaction products containrelatively unstable compounds, such as isobutylene, butadiene and thelike.

Two of the tubes may be connected in series, one being used forpreheating and the other as the reaction tube. The connection betweenthe two tubes is well insulated against heat loss.

In operation the flow of the gases or vapors in the heated reaction zoneis definitely infiuenced by each successive baffle. The linear velocityof the gases or vapors is alternatively high in the narrow passages l4,between the circumference of each bafiie and the tube wall, and low inthe larger zones l5 between the baflies and, at the same time, a rapidmovement of the gases in the zones IS, in relation to the heated wall ofthe tube, is substantially maintained, due to the formation of astanding eddy in each of these zones. In the rapid flow through thenarrow passages M, the gases in contact with the heated tube wall arecontinuously changcauses rapid heat exchange within the gas. Ow-

ing to the continued repetition of these successive operations maximumuniformity of heat distribution in the gas current is obtained and, atthe same time, the heat is most effectively transferred from the tubewall to the gases or vapors.

The increase in the rate of heat transfer between the hot walls and thegas undergoing treatment has been found, in some cases, to exceed and,at the same time, side reactions, such as the polymerization of olefinesto liquids and tar and the formation of free carbon, have beencompletely eliminated even when the fraction of the initial paraflinconverted on one passage through the reaction zone is as high as 80% andthe concentration of olefines in the product is in excess of 40% byvolume. As a comparison, it may be stated that if the gas is passedthrough an open reaction tube at a similar rate, it is found that theformation of by-products begins when the per-- centage decomposition ofthe gas is about 30 and the concentration of olefines in the product isbetween 20 and 25%.

The following examples are illustrative of the operation of theinventiom (1) Two tubes of the character described having an internaldiameter of 2.5 cm. and 40 cm. of heated section are connected inseries. The bafiies in the tubes are 2.2 cm. in diameter, spaced 1.4 cm.apart upon a rod 0.7 cm. in diameter. Ethane is passed through the tubesat the rate of 840 litres per hour. The heating is so controlled thatthe wall temperature at the exit end of the preheating tube andthroughout the length of the reaction tube is 940 C. Under theseconditions there are obtained 1340 litres per hour of a gas containing33.1% by volume of ethylene and 34.2% by volume of hydrogen.

(2) Propane is passed at the rate of 840 litres per hour through tubesas described in the previous example and the wall temperature at theexit end of the preheating tube and throughout the length of thereaction tube is maintained at 947 C. There are thus produced 1510litres per hour of a gas containing 26.1% by volume of ethylene and11.7% by volume of propylene, 71.5% of the entering propane beingconverted to olefines and the yield of olefines being 820! grams perhour with a current consumption of 1.5 k.w. hours per pound of olefines.

(3) 800 litres per hour of N-butane passed through similar tubes atcorresponding temperatures of 915 C. give 1515 litres per hour of a gascontaining 15.8% by volume of ethylene, 17.8% by volume of propylene and5.3% by volume of butylenes. This is a yield of 995 grams of olefinesper hour with a current consumption for heating purposes of 1.35 k. w.hours per pound of olefines.

(4) Hexane, containing about 40% 2-methyl pentane, 20% S-methyl pentane,30% n-hexane and 10% of other hydrocarbons, is passed at the rate of 905grams per hour through a single tube as described in Example 1 heated toa wall temperature at the exit end of 952 C. The product is 694 litresper hour of a gas containing 29.0% by volume of ethylene, 19.7% byvolume of propylene and small amounts of butylenes and butadiene. Theyield of olefines is 544 grams per hour with a current consumption of1.08 k. w. hours per pound of olefines.

(5) A mixture of litres of dipentene vapor diluted with 300 litres ofcarbon dioxide is passed, per hour, through the apparatus of Example 1with the temperature of the preheater at 390 C. and that of the reactiontube at 740 C. Isoprene is produced at the rate of 77 grams per hour. Aconsiderable amount of unchanged dipentene is recovered.

(6) A mixture of 57.7 litres of cyclo-hexane vapor diluted with 196litres of carbon dioxide is passed, per hour, through a reaction tube2.0 cm. in diameter, with 1.7 cm. diameter bafiies mounted on a 0.5 cm.diameter rod. The tube is heated to 895 C. over a length of 30 cm. Thereare obtained per hour 68.4 grams of butadiene with 47. grams unchangedcyclohexane.

While the invention has been described with particular reference tospecific examples, it will be apparent that it may be widely used invaporphase cracking or other thermal treatments of gases or vapors wherethe rate and uniformity of heat transfer are of particular importance.

Electrical heating as described has advantages particularly in relationto heat control but the use of natural gas or other gaseous, liquid orsolid fuels may be more economical under certain local conditions.

It will be observed that location of the solid disc bafliesperpendicularly to the axis of the reaction zone completely obstructs adirect flow of the gases through the central portion of the zone andprovides for a maximum sweeping action of the heated wall, thuscontinuously changing the gas layer in contact with the heated wall. Theincreased velocity at successive points produces a high degree ofturbulence in the gas current and the larger zones between the bafliesoffer repeated opportunity for uniform distribution of the heat in thegas.

This application is a division of copending application Serial Number658,098 filed February 23, 1933.

We claim:

1. Apparatus for the thermal treatment of gases which comprises anexternally heated reaction chamber having a heated wall and a pluralityof spaced baiiles in said chamber all of which are arranged to provide aplurality of narrow unobstructed annular passages between said baiiiesand the heated wall of said chamber and an eddy-forming zone betweeneach successive pair of baiiies.

2. Apparatus for the thermal treatment of gases which comprises anexternally heated reaction chamber and a plurality of spaced bafllestherein, all of said baflies being arranged on and at right angles tothe axis of said chamber and providing a plurality of narrowunobstructed annular passages between the heated wall of said chamberand said baflles.

3. Apparatus for the thermal treatment of gases which comprises acylindrical reaction chamber, means for externally heating said chamberand a plurality of circular discs therein, all said discs being arrangedat right angles to and on the axis of said chamber, said discs forming aplurality of narrow unobstructed annular passages adjacent the wall ofthe chamber and a plurality of temperature equalizing chambers betweensuccessive pairs of said baflles.

4. Apparatus for the thermal treatment of gases which comprises acylindrical reaction chamber having a gas inlet and a gas outlet, than;-that of the chamber to provide between means for externally heating thechamber, a each battle and the heated wall of the chamber plurality ofcircular baffles in said chamber and an unobstructed annular passagethrough which a rod arranged at the axis of the chamber, all all thegases must pass.

said circular baflies being mounted on said rod at spaced points andperpendicular thereto, the ADRIEN CAMERON. diameter of said bafllesbeing somewhat smaller COLIN H. BAYLEY.

